“In situ particle measurements in difficult environments: Examples from a supersonic jet with ice crystals, 250 Mw coal-fired combustor, and hydrofluoric acid aerosol”

1988 ◽  
Author(s):  
D. J. Holve
Keyword(s):  
Hydrofluoric Acid ◽  
Supersonic Jet ◽  
Ice Crystals ◽  
Particle Measurements

scholarly journals Convective formation of pileus cloud near the tropopause

2006 ◽  
Vol 6 (5) ◽  
pp. 1185-1200 ◽  
Author(s):  
T. J. Garrett ◽  
J. Dean-Day ◽  
C. Liu ◽  
B. Barnett ◽  
G. Mace ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Deep Convection ◽  
Cloud Microphysics ◽  
In Situ Measurements ◽  
Ice Crystals ◽  
Total Water ◽  
Wave Analysis ◽  
Cold Temperatures ◽  
Face Experiment

Abstract. Pileus clouds form where humid, vertically stratified air is mechanically displaced ahead of rising convection. This paper describes convective formation of pileus cloud in the tropopause transition layer (TTL), and explores a possible link to the formation of long-lasting cirrus at cold temperatures. The study examines in detail in-situ measurements from off the coast of Honduras during the July 2002 CRYSTAL-FACE experiment that showed an example of TTL cirrus associated with, and penetrated by, deep convection. The TTL cirrus was enriched with total water compared to its surroundings, but was composed of extremely small ice crystals with effective radii between 2 and 4 μm. Through gravity wave analysis, and intercomparison of measured and simulated cloud microphysics, it is argued that the TTL cirrus originated neither from convectively-forced gravity wave motions nor environmental mixing alone. Rather, it is hypothesized that a combination of these two processes was involved in which, first, a pulse of convection forced pileus cloud to form from TTL air; second, the pileus layer was punctured by the convective pulse and received larger ice crystals through interfacial mixing; third, the addition of this condensate inhibited evaporation of the original pileus ice crystals where a convectively forced gravity wave entered its warm phase; fourth, through successive pulses of convection, a sheet of TTL cirrus formed. While the general incidence and longevity of pileus cloud remains unknown, in-situ measurements, and satellite-based Microwave Limb Sounder retrievals, suggest that much of the tropical TTL is sufficiently humid to be susceptible to its formation. Where these clouds form and persist, there is potential for an irreversible repartition from water vapor to ice at cold temperatures.

In Situ ATR−FTIR Analysis of Surfactant Adsorption onto Silicon from Buffered Hydrofluoric Acid Solutions

Langmuir ◽  
2000 ◽  
Vol 16 (8) ◽  
pp. 3636-3640 ◽  
Author(s):  
A. Marcia Almanza-Workman ◽  
Srini Raghavan ◽  
Roger P. Sperline
Keyword(s):  
Hydrofluoric Acid ◽  
Surfactant Adsorption ◽  
Acid Solutions ◽  
Ftir Analysis

scholarly journals Ultrathin Tropical Tropopause Clouds (UTTCs): I. Cloud morphology and occurrence

2003 ◽  
Vol 3 (4) ◽  
pp. 1083-1091 ◽  
Author(s):  
Th. Peter ◽  
B. P. Luo ◽  
M. Wirth ◽  
C. Kiemle ◽  
H. Flentje ◽  
...  
Keyword(s):  
Gas Phase ◽  
Large Scale ◽  
Lower Stratosphere ◽  
Western Indian Ocean ◽  
Ice Crystals ◽  
Mixing Ratio ◽  
Efficient Point ◽  
Tropical Tropopause ◽  
Cold Point

Abstract. Subvisible cirrus clouds (SVCs) may contribute to dehydration close to the tropical tropopause. The higher and colder SVCs and the larger their ice crystals, the more likely they represent the last efficient point of contact of the gas phase with the ice phase and, hence, the last dehydrating step, before the air enters the stratosphere. The first simultaneous in situ and remote sensing measurements of SVCs were taken during the APE-THESEO campaign in the western Indian ocean in February/March 1999. The observed clouds, termed Ultrathin Tropical Tropopause Clouds (UTTCs), belong to the geometrically and optically thinnest large-scale clouds in the Earth's atmosphere. Individual UTTCs may exist for many hours as an only 200--300 m thick cloud layer just a few hundred meters below the tropical cold point tropopause, covering up to 105 km2. With temperatures as low as 181 K these clouds are prime representatives for defining the water mixing ratio of air entering the lower stratosphere.

Large Area Supersonic Jet Epitaxy of AlN, GaN, and SiC on Silicon

1996 ◽  
Vol 449 ◽  
Author(s):  
L.J. Lauhon ◽  
S. A. Ustin ◽  
W. Ho
Keyword(s):  
Supersonic Jet ◽  
X Ray Diffraction ◽  
Large Area ◽  
Free Jets ◽  
X Ray ◽  
Force Microscopy ◽  
Atomic Force ◽  
Supersonic Jet Epitaxy ◽  
Carrier Gases

ABSTRACTAlN, GaN, and SiC thin films were grown on 100 mm diameter Si(111) and Si(100) substrates using Supersonic Jet Epitaxy (SJE). Precursor gases were seeded in lighter mass carrier gases and free jets were formed using novel slit-jet apertures. The jet design, combined with substrate rotation, allowed for a uniform flux distribution over a large area of a 100 mm wafer at growth pressures of 1–20 mTorr. Triethylaluminum, triethylgailium, and ammonia were used for nitride growth, while disilane, acetylene, and methylsilane were used for SiC growth. The films were characterized by in situ optical reflectivity, x-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE).

scholarly journals Development of a Freeze-Drying Stage for In-Situ µ-CT Measurements

Processes ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 869
Author(s):  
Mathias Hilmer ◽  
Sebastian Gruber ◽  
Petra Foerst
Keyword(s):  
Process Parameters ◽  
Atmospheric Pressure ◽  
Freeze Drying ◽  
Pressure Range ◽  
Neutron Imaging ◽  
Ice Crystals ◽  
Controlled Environment ◽  
Sample Holder ◽  
Ct Measurements

This paper shows the development of a freeze-drying stage for in-situ μ-CT measurements. The stage can operate in a temperature range of −40 °C up to 70 °C, and a pressure range from atmospheric pressure to 7 Pa at the sample holder. To get the best visualization of the probe, it is fundamental that the materials around the sample holder are not absorbing most of the radiation. For this reason, we built an axial symmetrical stage built out of polyetheretherketon (PEEK). A test of the stage by different freeze-drying experiments with maltodextrin and sucrose particles and solutions demonstrated its suitability to visualize the freeze-drying processes in-situ. It was possible to track the drying front during the process by radiographic and tomographic measurements, as well as to visually resolve the ice crystals and porous structure in tomographic measurements. Using different samples and process parameters, we showed that the freeze-drying stage is not only suitable for in-situ µ-CT measurements, but also allows us to use the stage for other imaging methods such as neutron imaging, and for any sample where a controlled environment is needed.

In Situ Detection of Trace Levels of Copper in Hydrofluoric Acid

2000 ◽  
Vol 147 (6) ◽  
pp. 2337 ◽  
Author(s):  
A. J. Reddy ◽  
J. Michel ◽  
B. Parekh ◽  
J.-H. Shyu ◽  
L. C. Kimerling
Keyword(s):  
Hydrofluoric Acid ◽  
In Situ Detection
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